Up to recently, many input methods and character arrangements have been proposed to support ‘character inputting’ on portable devices such as cellular phone, PDA, remote controller, both having a limited number of buttons. But, since the portable device was not made originally for inputting characters and the function of inputting character was just added later to enhance its performance, it is more uncomfortable than PC keyboard. The portable device adopts 3×4 arranged buttons or alphanumeric keypads as an input means. The alphanumeric keypad has a limited number of buttons less than the PC keyboard. It is conventional to assign more than two characters on single button in order to overcome this limitation such that the user must push more than at least two buttons to select a character to be inputted.
Up to now, various character arrangements, input methods and input devices have been developed to improve the efficiency of inputting characters by using alphanumeric keypad. Although some of developed methods can enhance the input speed and the user convenience, there is a burden that the user is compelled to learn the new character arrangement. Namely, the all of developed methods bring a new character arrangement or an increase in buttons. Thus, in order to adopt a new input method, the user has to be acquainted with the input method and the character arrangement at the same time, and the manufacturer has to make some changes in the structure of portable device, especially in the number of buttons. Since the user hesitates to buy a portable device with unaccustomed input method, if only one of input method and character arrangement is changed, the burden will be smaller. Especially, from the user's point of view, it needs more time to learn the character arrangement than the input method. It means that the manufacturer can apply various input methods to the portable device without changing the accustomed character arrangement and the user can select input method fitting for himself.